Help:two isp3 servers primary and secondary dns

I have isp3 server at home.(mydns)
Now I setting up idp3 server @ work.(BIND)

How I can set them up so they function as redundant dns servers to each other?

So far I use configuration on my home server that ns1 and ns2 points to the same isp3 server to .So there is no redundancy only it appears that I have two dns servers.I set it up this way just to experiment with it.I could get away with one dns record as NS1.

But @ work i would like to have it set up properly as it should be with primary and secondary dns.

So I wonder if both location/domains can function as redundant dns servers to each other.

could you please explain How it works in nut shell and how it needs to be set up to make it work so when aether servers goes down the one standing will still function on its own but when both servers are up there is two dns servers available to resolute requests.